No search was conducted on the subject matter of this specification in the U.S. Patent and Trademark Office or in any other search facility. In the prosecution of my aforementioned U.S. application Ser. No. 548,070, the U.S. Patent Office cited the following materials: U.S. Pat. No. 3,579,452; French Pat. No. 2,380,224; and pages 274-280 of a book entitled Inorganic and Theoretical Chemistry, Vol. 12, Longmans, Green & Co., N.Y., 1932. I am unaware of any other prior art more relevant to the subject matter of this specification.
Ford Motor Company, the assignee of this application, is also the assignee of two patent applications which deal with modified electrode materials for a rechargeable manganese dioxide cell. These applications are: "Rechargeable Manganese Dioxide Electrode Material-I", filed Aug. 8, 1983, Ser. No. 521,473; and "Rechargeable Manganese Oxide Electrode Materials", filed Aug. 8, 1983, Ser. No. 521,474. These two applications are hereby incorporated by reference.
Briefly, the first application is directed to an improved manganese dioxide electrode material, the material being one which may be cycled between discharged and charged states at higher utilization of reactant and for substantially greater number of cycles than previously known manganese dioxide electrode materials. The improved manganese dioxide electrode material is characterized in that a heavy metal selected from the group consisting of bismuth, lead, and mixtures of bismuth and lead is included in the electrode material by means of a chemical reaction.
The second application is directed to improved manganese oxide electrode materials. The manganese oxide electrode materials may be cycled between discharged and charged states at higher utilization of reactant and for a substantially greater number of cycles than previously known manganese dioxide electrode materials. The manganese oxide electrode materials are characterized in that a heavy metal selected from the group consisting of bismith, lead, and mixtures of bismuth and lead is included in the electrode material without initial reaction of the electrode components.
The method taught in application Ser. No. 521,473 for chemically incorporating bismuth, lead, and mixtures of bismuth and lead into the manganese dioxide electrode materials was a very cumbersome and expensive method. The purpose of this specification is to disclose and claim a relatively simple manner of making the improved manganese dioxide electrode material formed as a so-called "birnessite compound" and having a heavy metal selected from the group consisting of bismuth, lead, and mixtures of bismuth and lead chemically included therein.
The method illustrated in the application Ser. No. 521,473 for the manufacture of the compound BiMn.sub.x O.sub.y was as follows.
The precursor NaMn.sub.x O.sub.y.ZH.sub.2 O was prepared according to the procedure given by Wadsley in JACS, Vol. 72, 1781 (1950), as follows. Solution A formed of 110 grams NaOH in 500 ml H.sub.2 O was cooled in an ice bath before being added slowly into a solution B of 60 grams Mn(NO.sub.3).sub.2.6H.sub.2 O in 400 ml of water that was held at 3.degree.-5.degree. C. The Mn(OH).sub.2 that precipitated out was slowly oxidized by passing oxygen through a fritted glass tube into the solution still held at 3.degree.-5.degree. C. for five hours with agitation followed by standing overnight. The solid was suction filtered and was washed 10 times with distilled water. It was dried over a warm plate at approximately 50.degree. C. for one day. The product was analyzed by ICP-AES and found to contain 48% Mn and 7.5% Na. An x-ray diffraction pattern showed that the major components are (Na.Mn).sub.4.Mn.sub.12 O.sub.28 .8H.sub.2 O, Na.sub.4 Mn.sub.14 O.sub.27.9H.sub.2 O, (ASTM XRD file #4-0095 and #23-1045, respectively) and a minor amount of Hausmanite. The surface area was determined by Krypton adsorption as 50 m.sup.2 /g.
The complex oxide, BiMn.sub.x O.sub.y.ZH.sub.2 O, was prepared by an ion exchange method. This is the heavy metal (bismuth) containing manganese dioxide material to be used as the improved manganese dioxide electrode material. One gram of the precursor, as prepared above, was shaken in 10 ml of solution containing 1.46 grams Bi(NO.sub.3).sub.2.5H.sub.2 O (about five times of the stoichiometric amount required) for 16 hours. After exchange, the solid was filtered and repeatedly washed with distilled water. It was dried again at temperatures slightly above 50.degree. C. The product thus prepared was found to contain 45.2% Mn, 15% Bi, and 0% Na. Its crystalline structure was identified by XRD as similar to that of Na-free birnessite (ASTM file #23-1239). The existence of this Bi-containing manganate (or birnessite) has not been previously reported in the literature. It is in this manner that the bismuth containing manganate compound was formed in order to make the rechargeable manganese dioxide electrode material which is described in that application in greater detail.
It is readily apparent that the above-described method of making a heavy metal/manganese dioxide compound was a very cumbersome and expensive one. It is a primary object of this invention to provide a relatively simple and efficient method of making a heavy metal/manganese dioxide birnessite compound which can be used as the electrode material in a rechargeable cell.